clock.3

<B>Digital的Unix操作系统VAX 4.2源码</B>

.\" SCCSID: @(#)clock.3	8.1	9/11/90
.TH clock 3 
.SH Name
clock \- report CPU time used
.SH Syntax
.B #include <time.h>
.PP
.B clock_t clock ( )
.PP
.B CLOCKS_PER_SEC
.SH Description
.NXR "clock subroutine"
.NXR "time" "reporting"
The
.PN clock
routine returns the amount of CPU time 
(in microseconds) used since the
first call to
.PN clock .
The time reported is the sum of the user and system times of the
calling process and its terminated child processes 
for which it has executed 
.MS wait 2
or 
.MS system 3 .
To determine the time in seconds, the value returned by
.PN clock
should be divided by the value of the macro CLOCKS_PER_SEC.
.PP
The resolution of the clock is 16.667 milliseconds.
.SH Restrictions
The value returned by
.PN clock
is defined in microseconds for compatibility with systems that have
CPU clocks with much higher resolution.
Because of this, the value returned
will wrap around after accumulating
only 2147 seconds of CPU time (about 36 minutes).
.SH See Also
wait(2), times(3), system(3)